Due to more restrictive safety regulation requirements and general market development trends, automotive industry have to establish more efficient passenger and pedestrian protection systems by means of improved active safety devices (e.g. multiple airbag solutions, more sophisticated restraint systems, adapted system deployment strategies, etc.). In general, such techniques needs to more lead time to be activated in order to provide the full protection capability and/or additional data to be deployed in a more dedicated way according to the crash situation. In case of a collision event it is therefore essential to identify strong impacts as early as possible, i.e. in best case at the time of first contact with the car bumper.
Up to now, impact characterization is accomplished by so-called up-front sensors (also known as “g-sensors”) located in the bumper area of the car, which detect crash-related acceleration effects caused by deformation and vibration. Although such sensor elements are well proven in various automotive applications, their detection efficiency is meanwhile hampered due to mechanically softer materials and design constraints of modern car front-ends in order to fulfil requirements related to pedestrian protection or energy savings.
Further, it is known to employ membrane switch sensors, which are usually integrated into the front or rear bumper of the car. These sensors are effective in fast detection of an impact and have a high sensitivity, but are characterized by an activation threshold. If a force or pressure acting on the sensor exceeds the threshold, the sensor is activated. I.e. although the first impact may be reliably detected, no information on the time evolution of the impact force can be gained from these sensors. Also, these sensors can be influenced by humidity and temperature. Finally, these sensors are usually large (e.g. 1500×20 mm) and when installed into a bumper, they require a straight integration with respect to the z (i.e. vertical) direction. However, a large sensor that may not be curved gives rise to integration problems.